Most currently used credit cards, personal identity cards, passes, season tickets, admission cards, bank-notes, cheques, etc. can be forged or falsified with little difficulty using modern reproduction methods. Accordingly, numerous attempts have been made to store authenticating information on such identifying cards, bank-notes and the like, to increase the difficulty of forgery. For example, authenticating information may be recorded in the form of magnetic or optical markings which can be read with the aid of a machine.
An effective, known method for protection against forgery is provided by a credit card which can be read with the aid of a machine, carrying a hologram which constitutes the holographic reproduction of a particular pattern of discrete light-spots. However, the reading of such holograms requires the use of expensive reading apparatus comprising a high-capacity light-source and sensitive light-receivers, since the transfer efficiency of the holograms is low, i.e., only a small proportion of the transmission energy reaches the light-receivers.
Also known is an identifying card having a diffraction screen which, in the reading apparatus, deflects the reading light-beam, produced by a laser, in a certain direction on to a single photo-detector. This arrangement does not, however, ensure satisfactory safety as regards forgeries, since even with low-quality imitations of the diffraction screen- perhaps by using other simpler optical elements -- it is possible to cause a sufficient amount of light to strike the photo-detector and to cause the latter to give an erroneous indication of authenticity.
The object of the present invention is to provide an apparatus for storing and reading authenticating information which combines the forgery protection afforded by holographic storage with the high transfer efficiency of the known system that uses a diffraction screen storage.
It is another object of the present invention to provide an inexpensive means and method for storing and reading information or, a carrier to provide a reliable indication of authenticity of the carrier or data associated therewith.
These and other objects and features of the invention will become apparent from the claims and from the following description when read in conjunction with the appended drawings.